The present invention relates to a method and apparatus for producing a master disk used in manufacturing information recording disks.
A "stamper" is a term of art describing a thin disk metal mold with an optical pattern on its main surface, used to form an optical disk, such as a compact disk or a laser disk (trade name). The stamper may be prepared according to the following method. An optical pattern is formed on a glass disk, having its surface coated with a photoresist layer by exposing the photoresist layer to laser light modulated with a recording signal and then developing the exposure. Then, electrical conductivity is provided by any suitable means, such as Ag sputtering, Ni evaporating deposition or the like; and Ni is thickly applied by electrocasting.
Electroless plating can be employed for providing the electrical conductivity. The electroless plating is superior to Ni evaporating deposition in abrasion-resistance and corrosion-resistance of the stamper thus prepared. The application of electroless plating a method for producing a master disk for analog records is disclosed in Japanese Patent Application Nos. 46-33500 and 52-160613 by CBS SONY GROUP INC. Because an optical disk has very fine pit rows or guide grooves (track pitch: 1.6.mu.m) formed in its surface as compared with the sound grooves (track pitch: about 100.mu.m) of the analog record, it is more important, in the case where electroless plating is used for producing a stamper, to improve manufacturing precision so that the recorded pit rows can be faithfully reproduced.
An electroless plating method as illustrated in FIG. 1 has been used for subbing treatment of a magnetic hard disk. The operation of the conventional apparatus illustrated in FIG. 1 is as follows. First, a disk 1 to be plated is mounted to a rotary jig 2. Then the jig 2 is moved over a first pretreating solution tank 3 (for example, a sensitizer solution such as a stannous chloride solution), a second pretreating solution tank 4 (for example, an activator solution such as a palladium, chloride solution), a washing tank 5 (pure water) and an electroless plating tank 6 so that the disk 1 together with the jig 2 are soaked in these tanks successively, along the course of the two-dotted chain line shown in FIG. 1. The disk 1 is rotated in the respective tanks to accomplish the plating process.
The first and second pretreating solutions are used in various combinations depending on the quality and property of the disk to be plated, and the pretreating solution tanks to be used may be increased in number to three or more.
The number of washing tanks 5 is not limited to the specific illustration in FIG. 1. For example, one washing tank 5 may be arranged between adjacent treating tanks so that the respective treating solution are not mixed with each other, or two washing tanks 5 may be arranged between adjacent treating tanks in order to more completely wash the disk between pretreatment tanks. The term "treating solution" herein used means a liquid, such as a pretreating solution, a plating solution, a cleaning solution and the like, to be used in a plating process.
A typical treating process (hereinafter called "AD process") according to the electroless plating method using the aforementioned apparatus for subbing treatment of a magnetic disk is carried out by successively executing the following steps (1)-(13) with respect to a blank disk.
(1) Cleaning step
(2) Washing step
(3) Etching step
(4) Washing step
(5) Zinc replacing step
(6) Washing step
(7) Pickling step
(8) Washing step
(9) Zinc replacing step
(10) Washing step
(11) Surface adjusting step
(12) Washing step
(13) Electroless plating step
In the cleaning step (1), the disk 1 mounted to the rotary jig 2 is put into the first treating tank (the pretreating solution tank 3 in FIG. 1) together with the jig 2, to the disk 1 while it is rotated by a driving means, such as a motor, provided on the jig. The the rotation of the disk 1 through the jig not only uniformly treats the disk surface but also removes impurities deposited on the disk.
After the cleaning step, the rotary jig 2 with the disk 1 is moved into the second treating tank (the washing tank 5 in FIG. 1), by a conveying means (not shown) or manually so as to carry out the washing step (2). In the second treating tank, the disk 1 is treated in the same manner as in the cleaning step. After the washing step, the disk is similarly treated successively in the etching step (3), in the washing step (4). . . , thereby completing all the steps (1)-(13) described above.
Arranged in the manner described above, the conventional electroless plating apparatus is defective in that it is necessary at all times to keep the respective treating solutions clean. This requires a cleaning means, such as circulatory filtration, in that some treating solutions may deteriorate gradually so that it is difficult to perform uniform treatment at all times, and further in that the rotary jig 2 including movable parts is soaked in the treating solution impurities, such as jig flakes, foreign matters and the like are often suspended in the treating solution. Accordingly, the conventional apparatus is unsuited for precise electroless plating of a stamper.
Further, troublesome masking must be made in the case where only one side of the disk is to be treated, because the disk as a whole is soaked in the treating solutions.
Further, it is necessary at all times to add pure water because the treating solution is more or less brought into the washing tank 5 (pure water). Where a small number of disks are treated, pure water is thus used wastefully.
Further, it is necessary that precipitated plating matter be dissolved by an acid, because such precipitated plating matter is deposited on the rotary jig 2 when the jig is used in all the steps of the electroless plating method.
Further, the treating solution often overflows the tank when the jig 2 is moved from the treating tank to the washing tank, as the form of the jig 2 is complex. In addition, the conventional apparatus has other defects in that, for example, the treating solutions are easily dropped to the outside or scattered in the form of a mist during conveyance of the jig.